Unless otherwise indicated herein, the materials described in this section are not prior art to the claims and are not admitted to be prior art by inclusion in this section.
A typical cellular wireless network includes a number of base stations that radiate to define wireless coverage areas, such as cells and cell sectors, in which mobile stations such as cell phones, tablet computers, tracking devices, embedded wireless modules, and other wirelessly equipped communication devices, can operate. In turn, each base station may be coupled with equipment that provides connectivity with one or more transport networks. Such equipment may include a mobile switching center (MSC) or other serving system that is configured to provide connectivity with the public switched telephone network (PSTN) and/or the Internet for instance. With this arrangement, a mobile station operating in coverage of the network may engage in air interface communication with a base station and may thereby communicate via the base station with various remote network entities or with other mobile stations.
An MSC may also be designed to provide connectivity among multiple base stations under the control of the MSC. For example, the MSC may provide connectivity between a first mobile station that is served by a first base station under the control of the MSC and a second mobile station that is served by a second base station that is also under the control of the MSC. In a cellular wireless network that includes multiple MSCs, inter-MSC trunks may provide connectivity between mobile stations that are served by separate MSCs. For instance, to provide connectivity between a first mobile station that is served by a first MSC and a second mobile station that is served by a second MSC, the first MSC or the second MSC may establish a dedicated circuit on an inter-MSC trunk between the first MSC and the second MSC so that the first mobile station and the second mobile station may communicate. As an example, the inter-MSC trunk may be a T1 digital communications link.
In general, a cellular wireless system may operate in accordance with a particular air interface protocol or “radio access technology,” with communications from the base stations to mobile stations defining a downlink or forward link and communications from the mobile stations to the base stations defining an uplink or reverse link. Examples of existing air interface protocols include, without limitation, Code Division Multiple Access (CDMA) (e.g., 1×RTT and 1×EV-DO), Long Term Evolution (LTE), WiMAX, iDEN, TDMA, AMPS, Global System for Mobile Communications (GSM), GPRS, UMTS, EDGE, MMDS, WI-FI, and BLUETOOTH. Each protocol may define its own procedures for initiation of calls, handoff between coverage areas, and functions related to air interface communication.
In accordance with the air interface protocol, each coverage area may operate on one or more carrier frequencies and may define a number of air interface channels for carrying information between the base station and served mobile stations. These channels may be defined in various ways, such as through frequency division multiplexing, time division multiplexing, and/or code-division multiplexing for instance.
Furthermore, mobile stations may store a preferred roaming list (PRL), which includes a prioritized list of communication systems that the mobile station may access and/or not access. In a CDMA system for instance, a PRL is a database that assists a mobile station in the acquisition and selection of a serving CDMA network. For a CDMA 1×RTT system, a PRL includes (i) an acquisition table which lists the band and frequencies that the mobile station is to use when searching to acquire a system and (ii) a system table which identifies systems by a system identification code (SID) and network identification code (NID) pair. For a CDMA 1×EV-DO system, a PRL similarly includes an acquisition table and a system table. However, within the system table, 1×EV-DO systems are identified by a subnet ID as opposed to a SID, NID pair. Each CDMA base station broadcasts its SID, NID pair or subnet ID in system overhead messages. Thus, when a mobile station detects and allowed system, the mobile station may connect to the identified system.